The notation 2'-10 3/4" might seem a bit confusing.
In words, the length is 2 feet, 10 and three-quarter inches.
The carpenter cut 7/16" off one end.
This means the carpenter cut 7/16 of an inch off one end.
We can subtract 7/16" to find the new length of the board.
3/4" - 7/16"
= 12/16" - 7/16"
= 5/16"
Instead of 3/4", we now have 5/16" inches at the end.
The length of the board after cutting the piece off the end is:
2'-10 5/16"